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UBC Theses and Dissertations

Modeling of flow liquefaction and large deformations in tailings dams using material point method Lino Ramírez, Erick Alexander


The release of tailings and impounded water after dam breaches has had catastrophic consequences for the population and the environment. These events have gained the attention of the geotechnical community because they occur without warning, causing massive damage. Flow liquefaction of tailings materials has been the cause of instability of recent tailings dam failures. These disasters were initiated by the triggering event that led the system to experience flow liquefaction and large deformations. To predict the evolution of flow-type instabilities, designers usually carry out dam-break analyses that rely on fluid mechanics methods since conventional slope stability methods such as limit equilibrium and finite elements only provide information until the onset of failure. Such decoupling of the geomechanics-based analysis for stability and fluid mechanics-based analysis for dam-break is not desirable, given the recent advances in critical state soil mechanics, strain-softening material models, and large deformation analysis methods. Hence, there is a need to develop analyses that can simulate the failure initiation and the post-failure stage observed during tailings dam disasters. In the present study, the triggering and the subsequent motion have been analyzed in a unified framework for the case of a saturated upstream tailings dam. Two different triggers are considered: the increment of pore water pressure and the sudden loss of strength in the foundation. A critical state bounding surface plasticity model is used for the tailings. This model can reproduce the contractive brittle behavior of loose saturated tailings. A two-phase single-point formulation of the material point method (MPM) has been considered to simulate the whole deformation process. This method has recently increased its popularity as a tool to deal with large deformation problems in geotechnical engineering. The influence of the initial void ratio on system performance is evaluated. The current study shows the capabilities of MPM along with an advanced constitutive model in simulating the complex stress-deformation mechanism observed in tailings dam failures.

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